In your CSS you have this line:
o{background: #e5e5e5;margin:0;padding: 5px 10px;line-height: 1.3;text-align: center}
It looks like one of the culprit areas of code is here and only FF is reading the "<o>" tags...
<o align="center"><font color="#FFFFFF" face="Verdana, Arial, Helvetica, sans-serif" cellpadding="1">New
to nightclubtonight.com?</font><font color="#000000" face="Verdana, Arial, Helvetica, sans-serif" cellpadding="1"><a href="http://nightclubtonight.com/forum/policy.asp"><u>Register
Here<br><br>
</u></a></font></o>
The <o> tags are given a background color of #e5e5e5. Try removing the background color declaration from the CSS and see if that helps.